The San Diego Surf under-17 girls soccer team was finishing practice in preparation for this weekend’s Surf Cup tournament.

As players ran the length of the field during conditioning Wednesday, coach Ada Greenwood approached one of the exhausted girls and gave a reassuring pat as she gasped for air, hunched over with her hands on her knees. Minutes earlier, she had removed a knee brace that she wears during competition.

“Keep fighting,” Greenwood told Zoe Purcell, a forward and midfielder who has battled through more injuries in the last 21/2 years than most athletes encounter in a career.

In January 2011, as a freshman playing for Torrey Pines High, Purcell tore the anterior cruciate ligament and meniscus in her right knee, an injury that ultimately required four surgeries. Numerous comebacks ended when she reinjured the knee.

“I had no idea that it would be this lengthy and emotional of a roller coaster,” Purcell said of the recovery process.

Purcell, 16, who is undecided about playing as a senior at Torrey Pines this winter, has played for the Surf since she was on the U-9 team. Though she has been unable to compete much in recent years, she still makes it to every practice and game.

“It makes us know how loyal and how special of a teammate she is,” said Greenwood, who’s also the coach of the USD women’s soccer team. “When someone is that committed every second, even when they can’t play, it just says so much.”

Purcell, who often has served as captain of her club teams, said she never doubted her ability to come back.

“I never once thought I was never going to play soccer again,” Purcell said. “I had no intention of ever quitting.”

The Surf’s U-17 team is a member of the Elite Club National League. With the Surf facing some of the top girls clubs in the country this weekend, Greenwood plans to ease Purcell back into competition. Purcell said her knee feels fine, but the coach is concerned that her conditioning might not be up to speed.

“What I don’t want to do is make her play 60, 70 minutes in a row. That might be too much for her — not that she’ll hurt her knee, but she might pull a muscle or something,” Greenwood said.

Purcell and her teammates will open the Surf Cup against Juventus, a top-ranked team from Redwood City, at noon Saturday at the San Diego Polo Club.